Jumping between the two wireless networks to the third isn't complex. I believe someone already mentioned DD-WRT and therein is the crux:
A wireless adapter can (generally) only connect to a single SSID at a time. The same generally holds true for an access point. If you have one capable of it, and running White Russian or DD-WRT or whatever, it is possible that you could connect to an access point, SSH into the AP, connect to the next wifi network in the range, and SSH to that AP. So long as there are no connection losses there is no theoretical maximum to this arrangement (much like chaining proxy connections together).
Assuming you have supported hardware between you and your other machines there is no reason you can't continue to do this. The odds of finding it are slim to none.
So, basics: If you can broadcast an SSID *and* connect to another SSID, you can chain it through. My AP is capable, most client cards are not, generally you will require two cards to do this (much like you need two connections to run a fakeap).
The possibilities are limitless really, but we're stepping away from anything even remotely pentesting theoretical, unless you somehow got permission to pentest an entire gated community or something.